Abstract

A family of high-fiber-count cable designs containing as many as 4000 optical fibers is being developed for B-ISDN applications in the Japanese subscriber loop.^1,2 The basic unit of the cable design (see Fig. 1) has a stack of 10 fiber ribbons, each containing 16 thinly coated optical fibers³ in a free-standing U groove (or U channel). The asymmetric U-groove cross section behaves quite differently during the cable-stranding process than does a typical loose-tube or slotted-core cable design. Our hypothesis is that a very rigid U groove will not conform properly to the central strength member during stranding because of U-groove torsional resistance. Such a rigid U groove will resist stranding symmetry, causing a helical-ribbon-length imbalance and increasing optical attenuation where the ribbon cannot assume its desired stranding position. As an example, Fig. 2 shows cross sections of U grooves stranded around an overcoated central strength member with and without a ribbon- helical-length imbalance. In Fig. 2(a) the radial distances from the cable center to fiber 1 and fiber 16 in the bottom ribbon are equivalent (r₁ = r₁₆). Radial distances from the cable center are not equivalent for r₁, and r₁₆ in Fig. 2(b) because of torsional resistance. In this study we examine the effect of U-groove torsional rigidity on cable performance for two similar size U grooves with different torsional rigidities.

© 1994 Optical Society of America